Explain EXPLAIN QUERY TREE (children 1)
 SelectWithUnionQuery (children 1)
  ExpressionList (children 1)
   SelectQuery (children 3)
    ExpressionList (children 1)
     Function uniq (children 1)
      ExpressionList (children 1)
       Identifier t.alias_of_a
    TablesInSelectQuery (children 1)
     TablesInSelectQueryElement (children 1)
      TableExpression (children 1)
       Subquery (alias t) (children 1)
        SelectWithUnionQuery (children 1)
         ExpressionList (children 1)
          SelectQuery (children 3)
           ExpressionList (children 2)
            Identifier a (alias alias_of_a)
            Function sum (children 1)
             ExpressionList (children 1)
              Identifier b
           TablesInSelectQuery (children 1)
            TablesInSelectQueryElement (children 1)
             TableExpression (children 1)
              TableIdentifier test_rewrite_uniq_to_count
           ExpressionList (children 1)
            Identifier alias_of_a
    Set
